Optical connector and a method of attaching the same

ABSTRACT

A short optical fiber 2 is incorporated in a ferrule 1 having a polished front end, so as to be projected from the rear end of the ferrule. In a base member 3 in which the short optical fiber is to be fitted into a hole 3b, a V-groove 3d to which the glass portion of an optical fiber is to be fixed, and a V-groove 3e to which the coated portion is to be fixed are formed. A cover member 4 is placed on the base member. The base member 3 and the cover member 4 are clamped by clamp members 5a and 5b and the base member 3 presses the V-grooves. Wedges which are not shown are pressingly inserted between recesses 3g and 4c, and 3h and 4d, and an optical fiber 10 is inserted from the rear portion. Thereafter, the wedges are detached and the optical connector is attached to the terminal of the optical fiber 10.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an optical connector for connecting opticalfibers to each other, and also to a method of attaching the opticalconnector.

2. Description of the Related Art

Conventionally, a connecting method is employed in which a short opticalfiber is previously attached to a ferrule of an optical connector and anoptical fiber to which the optical connector is to be connected is thenconnected to the short optical fiber. In the method, since the shortoptical fiber is previously attached to the ferrule, the front end ofthe ferrule can be previously polished under a state where an opticalfiber is attached. Therefore, it is not required to conduct a polishingwork during a work of attaching the optical connector to an opticalfiber, thereby producing an advantage that the work of attaching theoptical connector can be completed in a short time.

In each of optical connectors disclosed in Japanese patent publication(Kokai) No. SHO 63-186205, Japanese patent publication (Kokoku) No. HEI7-69498, and Japanese patent publication (Kokai) No. SHO 64-72105, ashort optical fiber of a ferrule is connected to an optical fiber towhich the connector is to be attached, by means of fusion or adhesion.The connection due to fusion has a problem in that a fusing apparatus isrequired, and that due to adhesion has a problem in that a prolongedtime period is necessary for conducting the adhesion work. In the casewhere an ultraviolet-setting resin is used in adhesion, there is anotherproblem in that an ultraviolet irradiator is necessary. When a fusingapparatus or an ultraviolet irradiator is used, there arises a furtherproblem in that a place for installing such an apparatus and a powersource must be ensured. Consequently, such methods are not alwayssuitable for a work in the field.

Japanese patent publication (Kokai) No. SHO 63-8613 discloses an opticalconnector having a cylindrical ferrule consisting of two capillaries.The optical connector is assembled while a short optical fiber ispreviously fixed to one of the capillaries, and the fixed optical fiberis inserted to the other small bore. The optical fibers are contactedwith each other in the small bore. Also an optical connector disclosedin Japanese patent publication (Kokai) No. HEI 6-337325 employs a methodin which an optical fiber to which the optical connector is to beconnected is contacted with a short optical fiber in a small bore of acapillary. In the case where a capillary is used as described above,since two optical fibers are not fixed in the coupling portion, there isa problem in that variation of the ambient temperature or an operationof handling the optical connector may easily cause misalignment and agap between the cores of the optical fibers, which are main factors ofvariation of the optical loss.

By contrast, an optical connector proposed in Japanese patentapplication No. HEI 7-283420 has a configuration in which asemispherical space is formed at a center portion of a ferrule, a shortoptical fiber and an optical fiber to which the optical connector is tobe attached are butted together on the ferrule and in the space, and aholding member is fixed to the space, thereby pressing the opticalfibers. In the optical connector, fusion and adhesion are not conducted,and hence a fusing apparatus is not necessary and a time period ofconducting an adhesion work is not required. Therefore, the proposedoptical connector has an advantage that the work of connecting opticalfibers together can be completed in a short time. Since the couplingportion of the two optical fibers is pressed by the holding member,moreover, there is an advantage that the coupling state can be ensured.However, the optical connector has the following problem. Since aferrule of a special structure is used, a groove in which optical fibersare butted together is a half-round groove having a shape which isformed by splitting an optical fiber hole into halves. Consequently, theaxial misalignment is larger in degree as compared with the case where aV-groove is used.

SUMMARY OF THE INVENTION

The invention has been conducted in view of the above-mentionedcircumstances. It is an object of the invention to provide an opticalconnector which can be easily attached to an optical fiber and in whichthe attaching work can be completed in a short time and the opticalfiber can be surely coupled with a short optical fiber.

According to the invention, an optical connector comprises: a ferrulewhich incorporates a short optical fiber in a small bore which is formedalong a center axis, the short optical fiber being projected from a rearend of the ferrule, the ferrule having a polished front end face; a basemember having a holding portion which holds the rear end of the ferrule,and an optical fiber positioning and fixing groove which is formed in anupper face to be continuous with the small bore; a cover member whichpresses an optical fiber against the optical fiber positioning andfixing groove; and a clamp member which presses the cover member towardthe base member, the connector further comprising a wedge insertionportion into which a wedge for pressingly separating the cover memberand the base member from each other can be inserted.

According to the invention, in the optical connector of the firstaspect, the cover member presses an optical fiber to be attached to theoptical connector, toward the base member and against the optical fiberpositioning and fixing groove at two portions, i.e., a portion where theshort optical fiber is connected with the optical fiber to be attached,and a coated portion of the optical fiber to be attached.

According to the invention, the wedge insertion portion is disposed soas to pressingly separate the cover member and the base member from eachother at the two portions i.e., the portion where the short opticalfiber is connected with the optical fiber to be attached, and the coatedportion of the optical fiber to be attached.

According to the invention, the optical fiber positioning and fixinggroove formed in the base member has a V-like section shape.

According to the invention, the optical fiber positioning and fixinggroove formed in the base member has a trapezoidal section shape.

According to the invention, the short optical fiber has amirror-finished rear end.

According to the invention, the front end face of the ferrule ispolished into a spherical shape.

According to the invention, the front end face of the ferrule isobliquely mirror-polished.

According to the invention, the front end face of the ferrule ismirror-polished in a direction perpendicular to an optical fiber axis.

According to the invention, the base member is made of a substancehaving a coefficient of linear expansion which is substantially equal toa coefficient of linear expansion of the optical fiber.

According to the invention, an outer periphery of the short opticalfiber is coated by a metal or carbon.

According to the invention, a space in which the optical fiber is freeis formed between a rear end of the small bore of the ferrule and afront end of a fiber presser which presses the short optical fiber andwhich is disposed on the base member.

According to the invention, a housing which can be fitted with an SCtype optical connector is attached to the optical connector.

According to the invention, the wedge can be inserted or detached undera state where a housing is assembled.

According to the invention, an outer periphery of a rear end face of theshort optical fiber is chamfered.

According to the invention, a size of the chamfer of the short opticalfiber is not smaller than 10 μm.

According to the invention, a work of chamfering the short optical fiberis conducted by an electric discharge.

According to the invention, a method of attaching an optical connectoruses the above-mentioned optical connector, and comprises the steps of:inserting the wedge into the wedge insertion portion, thereby forming aspace into which the optical fiber can be inserted, between the basemember and the cover member; inserting the optical fiber from a rearside of the optical connector until the optical fiber abuts against theshort optical fiber; and detaching the wedge, thereby attaching theoptical connector to a terminal of the optical fiber.

According to the invention, the optical connector is assembled while acylindrical member having an outer diameter which is substantially equalto an outer diameter of the short optical fiber is disposed so as to becontinuous with a rear end of the short optical fiber, above the opticalfiber positioning and fixing groove.

According to the invention, the cylindrical member is a silica opticalfiber.

According to the invention, a method of attaching an optical connectoruses the above-mentioned optical connector, and comprises the steps of:inserting the wedge into the wedge insertion portion, thereby removingthe cylindrical member; inserting the optical fiber from a rear side ofthe optical connector until the optical fiber abuts against the shortoptical fiber, into a space which is formed between the base member andthe cover member by the insertion of the wedge and into which theoptical fiber can be inserted; and detaching the wedge, therebyattaching the optical connector to a terminal of the optical fiber.

According to the invention, the optical connector is assembled while adummy member is pressingly held between the cover member and the basemember, thereby preventing the cover member and the base member fromsubstantially applying a pressing force on the short optical fiber.

According to the invention, a method of attaching an optical connectoruses the above-mentioned optical connector, and comprises the steps of:removing the dummy member; inserting the wedge into the wedge insertionportion, thereby forming a space into which the optical fiber can beinserted, between the base member and the cover member; inserting theoptical fiber from a rear side of the optical connector until theoptical fiber abuts against the short optical fiber; and detaching thewedge, thereby attaching the optical connector to a terminal of theoptical fiber.

According to the invention, in a method of attaching an opticalconnector, the space which is formed by holding the dummy member in theabove-mentioned optical connector and which is between the base memberand the cover member is configured so that the optical fiber can beinserted into the space, and the method comprises the steps of:inserting the optical fiber from a rear side of the optical connectoruntil the optical fiber abuts against the short optical fiber; anddetaching the dummy member, thereby attaching the optical connector to aterminal of the optical fiber.

According to the invention, an optical connector comprises a ferrulewhich incorporates a short optical fiber and which has a polished frontend face, an outer periphery of a rear end face of the short opticalfiber being chamfered.

According to the invention, an optical connector comprises: a ferrulewhich incorporates a short optical fiber in a small bore which is formedalong a center axis, the short optical fiber being projected from a rearend of the ferrule, the ferrule having a polished front end face; a basemember having a holding portion which holds the rear end of the ferrule,and an optical fiber positioning and fixing groove which is formed in anupper face to be continuous with the small bore; a cover member whichpresses an optical fiber against the optical fiber positioning andfixing groove; and a clamp member which presses the cover member towardthe base member, an outer periphery of a rear end face of the shortoptical fiber being chamfered.

According to the invention, a size of the chamfer of the short opticalfiber is not smaller than 10 μm.

According to the invention, a work of chamfering the short optical fiberis conducted by an electric discharge.

The above and other objects and features of the present invention willbe more apparent from the following description taken in conjunction theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C illustrate a first embodiment of the optical connector ofthe invention, where FIG. 1A is a side view, FIG. 1B is a plan view, andFIG. 1C is a section view taken along a plane perpendicular to the sheetof FIG. 1B;

FIG. 2 is a perspective view diagrammatically showing the structure ofmain portions of FIG. 1;

FIGS. 3A and 3B are section views illustrating a state where the opticalconnector is attached to an optical fiber;

FIGS. 4A and 4B are section views showing center portions of thesections taken along the lines B--B and C--C of FIG. 3A;

FIGS. 5A and 5B are diagrams illustrating a state in which a wedge isinserted;

FIG. 6 shows a modification of a cover member;

FIG. 7 show a modification of a clamp member;

FIG. 8 show another modification of the clamp member;

FIGS. 9A to 9C are diagrams illustrating a free space;

FIGS. 10A and 10B are diagrams illustrating a state where an opticalfiber positioning and fixing groove is deformed;

FIG. 11 is a diagram illustrating a second embodiment of the opticalconnector of the invention;

FIG. 12 is a diagram illustrating a third embodiment of the opticalconnector of the invention;

FIGS. 13A and 13B are diagrams illustrating a state where the opticalfiber positioning and fixing groove is deformed; and

FIGS. 14A, 14B and 14C are diagrams illustrating a fourth embodiment ofthe optical connector of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of preferred embodimentsof the invention with reference to the accompanying drawings.

FIGS. 1A to 1C and 2 illustrate a first embodiment of the opticalconnector of the invention. FIG. 1A is a side view, FIG. 1B is a planview, FIG. 1C is a section view taken along a plane perpendicular to thesheet of FIG. 1B, and FIG. 2 is a perspective view diagrammaticallyshowing the structure of main portions. In the figures, 1 designates aferrule, 1a designates a front end face, 2 designates a short opticalfiber, 3 designates a base member, 3a designates a flange, 3b designatesa hole, 3c designates a notched groove, 3d and 3e designate opticalfiber positioning and fixing grooves, 3f designates a flange, 3g and 3hdesignate recesses, 4 designates a cover member, 4a and 4b designatepressing portions, 4c and 4d designate recesses, 5a and 5b designateclamp members, 5c designates a notch, 6 designates a stop ring, 6adesignates an aperture, 7 designates a plug frame, 7a designates anaperture, 8 designates a coil spring, 9a and 9b designate wedgeinsertion holes, and 10 designates an optical fiber. In the ferrule 1, asmall bore into which an optical fiber can be inserted is opened alongthe center axis. The short optical fiber 2 is inserted into the smallbore and bonded thereto. The front end face 1a is polished so as to beperpendicular to the axis. The short optical fiber 2 is projected fromthe rear end of the ferrule 1. The rear end of the short optical fibermay not be processed after cutting. Alternatively, the rear end may bepolished so as to constitute a mirror finished surface in order toreduce the connection loss.

The finished state of the front end face of the ferrule is notrestricted to a mirror-polished surface which is perpendicular to theaxis as shown in FIGS. 1A to 1C. In the case where the front end face isobliquely mirror-polished, there is an advantage that the reflectedlight from the end face is diverged to the outside of the system.Alternatively, a PC (Physical Contact) coupling may be realized by aspheric working process.

The base member 3 and the cover member 4 is made by, for example, aliquid crystal polymer or an epoxy containing a filler of 70% or moretherein. The material of the member is not restricted to a liquidcrystal polymer. From the view point of temperature characteristics, asubstance having a coefficient of linear expansion which issubstantially equal to that of the glass of the optical fiber ispreferably used. The flange 3a is disposed at the front end of the basemember 3 and the circular hole 3b is formed in the flange. The rear endportion of the ferrule 1 is fitted into the circular hole 3b, therebycausing the ferrule 1 to be held by the base member 3. Alternatively,the ferrule and the base member are fixed together by an adhesive agent.In the flange 3a, the notched groove 3c is formed at an appropriateposition so as to prevent the optical connector from rotating when theoptical connector is connected to another optical connector or the like.The optical fiber positioning and fixing grooves 3d and 3e are formed inthe upper face of the base member 3. The optical fiber positioning andfixing groove 3d is a portion to which the glass portion of the shortoptical fiber 2 and that of an optical fiber to which the opticalconnector is to be attached are fixed. The groove is formed as aV-groove. Under the state where the ferrule 1 is held by the base member3, the rear end of the short optical fiber 2 is at a position in theoptical fiber positioning and fixing groove 3d. The arrow A of FIG. 1Cshows the position. The optical fiber positioning and fixing groove 3eis a portion to which the coated portion of the optical fiber to whichthe optical connector is to be attached is fixed. The groove is formedas a trapezoidal groove. As seen from FIG. 1C, the flange 3f which isformed in an intermediate portion of the base member 3 is a portionagainst which the coil spring 8 abuts. The rear end of the base member 3may have an appropriate shape.

The cover member 4 is used for pressing the optical fiber inserted intothe optical fiber positioning and fixing grooves, and consists of thepressing portion 4a which presses the portion in the optical fiberpositioning and fixing groove 3d, and the pressing portion 4b whichpresses the portion in the optical fiber positioning and fixing groove3e. In the embodiment, the pressing portions 4a and 4b are integrallyformed. Alternatively, the cover member may be divided into two parts sothat the pressing portions 4a and 4b are configured as separate members.

The clamp members 5a and 5b are used for exerting a spring force bywhich the cover member 4 is pressed toward the base member 3. In theembodiment, plate springs having a U-like section shape are used as theclamp members. As seen from FIGS. 1C and 2, the clamp member 5a appliesa spring force by which the pressing portion 4a of the cover member 4 ispressed toward the base member 3, and the clamp member 5b exerts aspring force by which the pressing portion 4b of the cover member 4 ispressed toward the base member 3. In the embodiment, the spring force ofthe clamp member 5b is divided into two parts by the notch 5c. The rearpart exerts a pressing force on the portion in the optical fiberpositioning and fixing groove 3e. The front part exerts a pressing forceon the portion in the optical fiber positioning and fixing groove 3d andin the rear of the position indicated by the arrow A.

The manner of assembling the optical connector will be described. Theferrule 1 is fitted into the hole 3b of the base member 3. With respectto the center axis of the ferrule 1 and the optical fiber positioningand fixing groove 3d, the upper face of the base member is defined sothat the glass portion of the optical fiber elongates along a line.Therefore, the short optical fiber projected from the rear end of theferrule 1 is inserted into the optical fiber positioning and fixinggroove 3d. The cover member 4 is placed on the base member, and theclamp members 5a and 5b are set, so that the cover member 4 is clampedonto the base member 3. When the cover member 4 is placed on the basemember 3, the recesses 3g and 3h shown in FIG. 2 which are formed bypartially removing away the base member 3 are joined with the recesses4c and 4d to form the wedge insertion holes 9a and 9b shown in FIG. 1A,respectively. In FIG. 1B, the hatched portions of broken lines show thepositions of the wedge insertion holes 9a and 9b. The coil spring 8 isthen fitted onto the members and the plug frame 6 and the stop ring 7are coupled together, thereby completing the optical connector as shownin FIGS. 1A to 1C. When the plug frame 6 is configured so as to coincidewith the SC type connector (a single-core optical fiber connector of theF04 type of JIS C 5973), the general versatility is enhanced.

In the plug frame 6 and the stop ring 7, the apertures 6a and 7a areopened in order to expose the wedge insertion holes 9a and 9b under thestate where the optical connector is assembled. In the work of couplingthe plug frame 6 and the stop ring 7 together, therefore, the couplingis conducted in a positional relationship in which the apertures 6a and7a respectively coincide with the wedge insertion holes 9a and 9b.

The optical connector which has been completed as described above isattached to the front end of the optical fiber. Before the attachment,wedges which are not shown are respectively inserted into the wedgeinsertion holes 9a and 9b so that the base member 3 and the cover member4 are separated from each other against the forces exerted by the clampmembers 5a and 5b. when the base member 3 and the cover member 4 areseparated from each other, the optical fiber 10 can be inserted from theside of the optical fiber positioning and fixing groove 3e as shown inFIG. 2. When the front end of the inserted optical fiber 10 advances toabut the rear end of the short optical fiber, the wedges are detached.As a result, the inserted optical fiber 10 can be fixed. Preferably, anindex matching material is applied to a part of the optical fiberpositioning and fixing groove 3d so that the rear end of the shortoptical fiber 2 abuts against the front end of the optical fiber 10 viathe index matching material.

FIGS. 3A to 3C illustrate the state where the optical connector isattached to the optical fiber. The figure is split into two portions,i.e., FIGS. 3A and 3B in such a manner that the portions partly overlapwith each other. The reference numeral 11 designates a protection tube,12 designates a boot. In the embodiment, the optical fiber 10 isconfigured by providing a glass fiber with a cover of anultraviolet-setting resin having an overall outside diameter of about0.25 mm. In the invention, the configuration of an optical fiber is notrestricted to this, and any appropriate additional protective cover madeof a resin such as nylon or the like may be applied thereto. When anoptical fiber which is not provided with a protective cover of nylon orthe like is used, there arises a problem in that the optical fiber iseasily broken at a rear end portion of an optical connector to which theoptical fiber is attached. Therefore, the protection tube 11 and theboot 12 are used. After the optical fiber 10 is passed through them, theoptical fiber 10 which is passed through the protection tube is insertedand fixed by using the wedges as described above. Thereafter, the frontend portion of the boot 12 is pressingly inserted into the rear end ofthe stop ring 7 so as to be engaged therewith.

FIGS. 4A and 4B show center portions of the sections taken along thelines B--B and C--C of FIG. 3A, respectively. In the figures, thecomponents identical with those of FIGS. 1A to 1C and 2 are designatedby the same reference numerals and their description is omitted.Referring to FIG. 4A, the optical fiber positioning and fixing groove 3d(FIG. 2) of the base member 3 is formed as a V-groove. The glass portionof an optical fiber which is not shown in the figures is housed in thegroove, and then pressed by the cover member 4. The pressing force isapplied by the clamp member 5a.

FIG. 4B shows a part on the side of the optical fiber positioning andfixing groove 3e (FIG. 2). The optical fiber positioning and fixinggroove 3e which is formed in the base member 3 has a trapezoidal sectionshape. A groove is formed also in the cover member 4, and the coatedportion of the optical fiber 10 is pressingly fixed by the clamp member5b. In this example, a groove is formed also in the cover member 4. Thisgroove is not always necessary.

The optical fiber positioning and fixing groove for fixing the glassportion of the optical fiber, and that for fixing the coated portionhave any appropriate section shape such as a V-like shape or atrapezoidal shape. The depth and width of the grooves are preferably setso that the center axis of the optical fiber and that of the ferrule areon the same line.

FIGS. 5A and 5B are diagrams illustrating the state in which a wedge isinserted. In the figure, the components identical with those of FIGS. 4Aand 4B are designated by the same reference numerals and theirdescription is omitted. As shown in FIG. 5A, a wedge 13 having athickness which is greater than the height of the wedge insertion hole9a is pressingly inserted into the wedge insertion hole 9a in thedirection of the arrow. When the wedge 13 is pressingly inserted, thebase member 3 and the cover member 4 are forcedly separated from eachother against the resilient force of the clamp member 5a as shown inFIG. 5B, thereby enabling the optical fiber 10 to be inserted betweenthem. After the optical fiber 10 is inserted to a predeterminedposition, the wedge 13 is detached. Then, the state returns to that ofFIG. 5A and the optical fiber is fixed to the optical fiber positioningand fixing groove 3d by the resilient force of the clamp member 5a. Awedge is similarly inserted also into the wedge insertion hole 9b ofFIG. 4B, so that the base member 3 and the cover member 4 are forcedlyseparated from each other, thereby facilitating the coated portion ofthe optical fiber 10 to be inserted between them. When the wedge isdetached, the optical fiber can be fixed.

FIG. 6 shows a modification of the cover member. In the modification,the pressing portion 4a which presses the portion in the optical fiberpositioning and fixing groove 3d (FIG. 2), and the pressing portion 4bwhich presses the portion in the optical fiber positioning and fixinggroove 3e (FIG. 2) are configured as separate members.

FIGS. 7 and 8 show modifications of the clamp member. In FIG. 2, theclamp member 5b is divided into two parts by the notch 5c. As shown inFIG. 7, the notch may not be formed. In FIG. 2, the clamp members 5a and5b are configured as separate members. As shown in FIG. 8, the clampmembers may be configured as a single member.

The short optical fiber 2 is projected from the rear end of the ferrule,and, under the state where the ferrule is fitted into the base member,inserted into the optical fiber positioning and fixing groove of thebase member. The optical fiber may be sometimes bent at the outlet ofthe ferrule and the inlet of the optical fiber positioning and fixinggroove. Such a case occurs when a production error causes the centeraxis of the ferrule to be misaligned with that of the optical fiberhoused in the V-groove serving as the optical fiber positioning andfixing groove. As a method of improving static fatigue properties due toa bend applied to the short optical fiber, therefore, a coating forreinforcing the short optical fiber may be employed. The coating may bea metal coating, a carbon coating, or the like.

Preferably, a free space is formed in order to prevent an extremebending force from being applied to the short optical fiber. FIGS. 9A to9C are diagrams illustrating such a free space. The hatched portions ofthe short optical fiber 2 are fixed by the ferrule and the V-groove,respectively. The amount of deviation between the center axes of thefixed portions is called the offset amount. In the configuration whereina space in which the portion of the short optical fiber 2 between thefixed portions takes a free path is produced, no large bending force isapplied to the short optical fiber 2. For example, the length L of thefree space is set to be 2 mm or longer in the case where the offsetamount is 0.02 mm, or 2.5 mm or longer in the case where the offsetamount is 0.03 mm. According to this configuration, even in a long-termuse, it is possible to prevent a trouble from occurring in the shortoptical fiber 2.

The free space may be produced so as to ensure the length L of the freespace by, for example, using one or both of the following methods: amethod in which a space is formed in the rear end portion of the ferrule1 as shown in FIG. 9B; and that in which the V-groove of the base member3 and the cover member are retracted from the rear end face of theferrule 1 as shown in FIG. 9C.

The optical connector of the embodiment is stored until it is used inthe filed, under a state where, as shown in FIGS. 1A to 1C, the shortoptical fiber 2 incorporated in the ferrule 1 and projected from therear end of the ferrule is pressed by the cover member 4 against theoptical fiber positioning and fixing groove 3d of the base member 3.

When the optical connector is stored under a state where the opticalfiber is always pressed against the optical fiber positioning and fixinggroove 3d of the base member 3, there is a possibility that the portionof the optical fiber positioning and fixing groove 3d which is contactedwith the optical fiber creeps to be deformed.

FIGS. 10A and 10B are diagrams illustrating a state where the opticalfiber positioning and fixing groove is deformed. Under the state wherethe cover member (not shown) exerts a small pressing force so that shortoptical fiber is merely contacted with the optical fiber positioning andfixing groove 3d as shown in FIG. 10A, the optical fiber positioning andfixing groove 3d is not deformed at the contact portions and the shortoptical fiber is at the position P. When the clamp member applies apressing force to the cover member, the pressing force is concentratedto the contact portions of the side walls of the optical fiberpositioning and fixing groove 3d with which the short optical fiber iscontacted. With the passage of time, a creep phenomenon occurs todepressingly deform the side walls. When the deformation advances, theposition of the optical fiber is lowered. As the deformation amountbecomes larger, the contact area between the short optical fiber and theoptical fiber positioning and fixing groove 3d is increased. Therefore,the pressing force per unit area is reduced and the advance rate of thedeformation is lowered. It is assumed that, in the case where deformedportions 14 are formed in the side walls by the short optical fiber 2 asshown in FIG. 10B, the short optical fiber is lowered to the position Qof FIG. 10A when the deformation amount is α. The center position of theshort optical fiber is lowered by a distance d from the position in thecase where the side walls are not deformed.

When the optical connector in which such deformation is produced isattached to the front end of the optical fiber as described withreference to FIGS. 3A, 3B and 4A, 4B, the short optical fiber isdeviated from the optical fiber which is to be attached to the opticalconnector, by the distance d which has been described with reference toFIG. 10A, because the optical fiber positioning and fixing groove in theportion where the optical fiber is to be attached is not deformed,resulting in the increased coupling loss. Embodiments which can copewith such deformation of the optical fiber positioning and fixing groovewill be described.

FIG. 11 illustrates a second embodiment of the optical connector of theinvention and is a section view taken along the line D--D of FIG. 1C.The stop ring 6 and the plug frame 7 are not shown in the figure. In thefigure, the components identical with those of FIGS. 5A and 5B aredesignated by the same reference numerals and their description isomitted. The reference numeral 15 designates a dummy member. In theembodiment, the dummy member 15 is inserted into the wedge insertionhole 9a. A dummy member may be inserted also into the wedge insertionhole 9b. The dummy member 15 is used for, during a period when theoptical connector is stored, separating the base member 3 and the covermember 4 from each other in order that the pressing force of the covermember 4 is not applied to the short optical fiber or, even when apressing force is applied, the pressing force is made lessened so thatno substantially pressing force is exerted on the short optical fiber.Under the state where the optical connector is stored, the use of thedummy member 15 prevents the optical fiber positioning and fixing groovefrom being subjected to a pressing force which may deform the groove.When the optical connector is attached to an optical fiber, therefore,the positional deviation between the short optical fiber and the opticalfiber is prevented from occurring.

The optical connector is attached to the optical fiber in the followingmanner. In the case where the dummy member 15 having a size similar tothat of the wedge described with reference to FIGS. 5A and 5B, theoptical fiber is inserted into the optical connector, and the dummymember 15 is then detached from the optical connector, whereby theoptical connector can be connected to the optical fiber. In the casewhere the dummy member 15 having a size at which, when the dummy member15 is attached to the optical connector, a gap sufficient for insertingthe optical fiber is not formed is used, the dummy member 15 is detachedfrom the optical connector when the connector is to be attached to theoptical fiber. Thereafter, the optical connector is attached to theoptical fiber by using the wedge described with reference to FIGS. 5Aand 5B.

FIG. 12 illustrates a third embodiment of the optical connector of theinvention and is a section view similar to FIG. 1C. In the figure, thecomponents identical with those of FIGS. 1A to 1C are designated by thesame reference numerals and their description is omitted. The referencenumeral 16 designates a cylindrical member. In the embodiment, thecylindrical member 16 serving as a cylindrical dummy member is insertedinto the optical fiber positioning and fixing groove at the rear end ofthe short optical fiber 2. Preferably, the cylindrical member 16 has ahardness and an outer diameter which are substantially equal to those ofthe short optical fiber. In the case where the short optical fiber is asilica optical fiber, it is preferable to use a silica optical fiber asthe cylindrical member 16. The cylindrical member 16 is attached to theoptical connector during the work of assembling the connector.

When the optical connector is to be connected to the optical fiber, awedge is inserted as described with reference to FIGS. 5A and 5B so asto forcedly separate the base member 3 and the cover member 4 from eachother, the cylindrical member 16 is detached from the connector, theoptical fiber to be connected is inserted, and the wedge is thendetached from the connector. As a result of the attachment of thecylindrical member 16, under the state where the optical connector isstored, a creep phenomenon occurs both in the portion of the opticalfiber positioning and fixing groove in which the short optical fiber 2is positioned, and that of the optical fiber positioning and fixinggroove in which the cylindrical member 16 is positioned, in the sameconditions. Therefore, no positional deviation is produced between theoptical fiber to be connected, and the short optical fiber.

The deformation of the optical fiber positioning and fixing groove whichhas been described with reference to FIGS. 10A and 10B is problematicalso in a deformation state in the vicinity of the rear end portion ofthe short optical fiber. FIGS. 13A and 13B are section views of theoptical fiber positioning and fixing groove and taken in a plane whichpasses the center axis of the short optical fiber and which is parallelwith the upper face of the base member, FIGS. 13A shows a state wherethe optical fiber has not yet been connected, and FIG. 13B shows a statewhere the optical fiber to be connected is positioned. In the figures, 2designates a short optical fiber, and 10 designates an optical fiber.When the short optical fiber 2 is pressed against the optical fiberpositioning and fixing groove and a creep phenomenon occurs, the portionof the optical fiber positioning and fixing groove with which the shortoptical fiber 2 is contacted is deformed and the position of fixing theshort optical fiber is lowered as described with reference to FIGS. 10Aand 10B. In the rear end portion of the short optical fiber 2, at thesame time when the side walls are depressed, a part of the materialconstituting the side walls is moved and a bulge portion 17 is formed inthe rear of the short optical fiber 2.

When the optical fiber 10 is positioned in the optical fiber positioningand fixing groove in which the bulge portion is formed, the bulgeportion 17 obstructs the positioning, so that a gap 18 is formed betweenthe short optical fiber 2 and the optical fiber 10 as shown in FIG. 13B,thereby increasing the coupling loss.

FIGS. 14A to 14C illustrate a fourth embodiment of the optical connectorof the invention. FIG. 14A is a section view of a part of a shortoptical fiber, FIG. 14B is a diagram illustrating a state where opticalfibers are connected together, and FIG. 14C is an enlarged view of apart of FIG. 14b. In the figures, the components identical with those ofFIGS. 13A and 13B are designated by the same reference numerals andtheir description is omitted. The reference numeral 19 designates achamfered portion. In the embodiment, the chamfered portion 19 is formedin the outer periphery of the rear end face of the short optical fiber 2as shown in FIG. 14A. The chamfered portion 19 may be formed by a methodsuch as that in which a grinding work using a grindstone is conducted,or that in which the surface is slightly fused by an electric discharge.

Since the chamfered portion 19 is formed on the short optical fiber 2,the formation of the bulge portion 17 is reduced in degree, and theformed bulge portion 17 can be accommodated in the periphery of thechamfered portion 19. Therefore, the optical fiber 10 can abut againstthe short optical fiber 2 as shown in FIGS. 14B and 14C. The formationof the chamfered portion 19 prevents the cover member and the basemember from being damaged. When the size m of the chamfered portion 19is set not to be smaller than 10 μm, the connector can be prevented frombeing adversely affected by the bulge portion 17.

Even though the short optical fiber 2 and the optical fiber 10 arebutted against each other while avoiding an adverse effect due to thebulge portion 17, the axial misalignment due to the lowered distance dwhich has been described with reference to FIG. 10A cannot be canceled.However, the optical fiber 10 is pressed by the cover member to belowered while deforming the optical fiber positioning and fixing groove.Therefore, also the axial misalignment can be canceled. In the casewhere aluminum or plastics is used as the material of the base member,particularly, the deformation rapidly advances. When the opticalconnector is attached to the optical fiber, therefore, the axialmisalignment can be canceled in a short time. Consequently, theembodiment is particularly effective in the case where the optical fiberpositioning and fixing groove is formed in such a material which iseasily plastically deformed.

As apparent from the description above, the optical connector of theinvention comprises: a ferrule which incorporates a short optical fiberin a small bore which is formed along a center axis, the short opticalfiber being projected from a rear end of the ferrule, the ferrule havinga polished front end face; a base member having a holding portion whichholds the rear end of the ferrule, and an optical fiber positioning andfixing groove which is formed in an upper face to be continuous with thesmall bore; a cover member which presses an optical fiber against theoptical fiber positioning and fixing groove; and a clamp member whichpresses the cover member toward the base member, the connector furthercomprising a wedge insertion portion into which a wedge for pressinglyseparating the cover member and the base member from each other can beinserted. Consequently, the optical fiber can be inserted only byinserting the wedge into the optical connector, and the opticalconnector can be attached to the front end of the optical fiber bydetaching the wedge. During a work of attaching the optical connector,therefore, it is not required to conduct works of grinding, fusion,adhesion, and the like, and the work of attaching the optical connectorcan be completed in a short time.

According to the invention, the cover member presses an optical fiber tobe attached to the optical connector, toward the base member and againstthe optical fiber positioning and fixing groove at two portions, i.e., aportion where the short optical fiber is connected with the opticalfiber to be attached, and a coated portion of the optical fiber to beattached. Therefore, the portion where the short optical fiber isconnected with the optical fiber to be connected can be fixed, and hencea stable connection state can be maintained. Furthermore, the attachmentof the coated portion can be firmly done.

According to the invention, the wedge insertion portion is disposed soas to pressingly separate the cover member and the base member from eachother at the two portions, i.e., the portion where the short opticalfiber is connected with the optical fiber to be attached, and the coatedportion of the optical fiber to be attached. After the connection of theoptical fibers is ensured, therefore, the coated portion can be fixed.

According to the invention, the optical fiber positioning and fixinggroove formed in the base member has a V-like section shape or atrapezoidal section shape. Therefore, it is possible to suppress theconnection loss due to the axial misalignment.

According to the invention, the short optical fiber has amirror-finished rear end. Therefore, it is possible to suppress theconnection loss and reflection return light at the point where the shortoptical fiber is connected with the optical fiber.

According to the invention, the front end face of the ferrule ispolished into a spherical shape, obliquely mirror-polished, ormirror-polished in a direction perpendicular to an optical fiber axis.Therefore, it is not required to polish the front end of the ferrule inthe field.

According to the invention, the base member is made of a substancehaving a coefficient of linear expansion which is substantially equal toa coefficient of linear expansion of the optical fiber. Therefore, it ispossible to suppress the loss variation due to a temperature change.

According to the invention, an outer periphery of the short opticalfiber is coated by a metal or carbon. Therefore, it is possible torealize reinforcement to a bend between the ferrule and the opticalfiber positioning and fixing groove.

According to the invention, a space in which the optical fiber is freeis formed between a rear end of the small bore of the ferrule and afront end of a fiber presser which presses the short optical fiber andwhich is disposed on the base member. Therefore, it is possible tosuppress an effect due to the axial misalignment between the ferrule andthe optical fiber positioning and fixing groove.

According to the invention, a housing which can be fitted with an SCtype optical connector is attached to the optical connector. Therefore,it is possible to provide an SC type connector which can be rapidlyassembled.

According to the invention, the wedge can be inserted or detached undera state where a housing is assembled. Therefore, it is possible toattach the optical connector to the optical fiber in a short time.

According to the invention, the chamfer formed on the outer periphery ofthe rear end face of the short optical fiber can suppress the formationof a bulge portion which may be produced in the groove in which theshort optical fiber is to be positioned, and allow the produced bulgeportion to be accommodated in the periphery of the chamfered portion.Furthermore, the portion with which the rear end portion of the shortoptical fiber is contacted can be made hardly damaged.

According to the invention, in the optical fiber positioning and fixinggroove under the state where the optical connector is stored, theportion to which the short optical fiber is fixed and that to which theoptical fiber to be connected are similarly deformed, Therefore, it ispossible to eliminate the axial misalignment between the optical fiberto be connected and the short optical fiber.

According to the invention, the cover member and the base member areprevented by the dummy member from substantially exerting a pressingforce on the short optical fiber. Therefore, the optical fiberpositioning and fixing groove is not deformed by the short opticalfiber.

According to the invention, a work of attaching the optical connector toa terminal of an optical fiber can be simplified and completed in ashort time.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiment was chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents.

What is claimed is:
 1. An optical connector comprising:a ferrule whichincorporates a short optical fiber in a small bore which is formed alonga center axis, said short optical fiber being projected from a rear endof said ferrule, said ferrule having a polished front end face; a basemember having a holding portion which holds said rear end of saidferrule, and an optical fiber positioning and fixing groove which isformed in an upper face to be continuous with said small bore; a covermember which presses an optical fiber against said optical fiberpositioning and fixing groove; a clamp member which presses said covermember toward said base member; and a wedge insertion portion into whicha wedge for pressingly separating said cover member and said base memberfrom each other can be inserted.
 2. An optical connector according toclaim 1, wherein said cover member presses an optical fiber to beattached to said optical connector, toward said base member and againstsaid optical fiber positioning and fixing groove at two portions wheresaid short optical fiber is connected with the optical fiber to beattached, and where a coated portion of the optical fiber to beattached.
 3. An optical connector according to claim 2, wherein saidwedge insertion portion is disposed so as to pressingly separate saidcover member and said base member from each other at the two portions,where said short optical fiber is connected with the optical fiber to beattached, and where the coated portion of the optical fiber to beattached.
 4. An optical connector according to claim 1, wherein saidoptical fiber positioning and fixing groove formed in said base memberhas a V-like section shape.
 5. An optical connector according to claim1, wherein said optical fiber positioning and fixing groove formed insaid base member has a trapezoidal section shape.
 6. An opticalconnector according to claim 1, wherein said short optical fiber has amirror-finished rear end.
 7. An optical connector according to claim 1,wherein said front end face of said ferrule is polished into a sphericalshape.
 8. An optical connector according to claim 1, wherein said frontend face of said ferrule is obliquely mirror-polished.
 9. An opticalconnector according to claim 1, wherein said front end face of saidferrule is mirror-polished in a direction perpendicular to an opticalfiber axis.
 10. An optical connector according to claim 1, wherein saidbase member is made of a substance having a coefficient of linearexpansion which is substantially equal to a coefficient of linearexpansion of the optical fiber.
 11. An optical connector according toclaim 1, wherein an outer periphery of said short optical fiber iscoated by a metal or carbon.
 12. An optical connector according to claim1, wherein a space in which the optical fiber is free is formed betweena rear end of said small bore of said ferrule and a front end of a fiberpresser which presses said short optical fiber and which is disposed onsaid base member.
 13. An optical connector according to claim 1, whereina housing which can be fitted with an SC type optical connector isattached to said optical connector.
 14. An optical connector accordingto claim 1, wherein said wedge can be inserted or detached under a statewhere a housing is assembled.
 15. A method of attaching an opticalconnector comprising a ferrule which incorporates a short optical fiberin a small bore which is formed along a center axis, said short opticalfiber being projected from a rear end of said ferrule, said ferrulehaving a polished front end face; a basemember having a holding portionwhich holds said rear end of said ferrule, and an optical fiberpositioning and fixing groove which is formed in an upper face to becontinuous with said small bore; a cover member which presses an opticalfiber against said optical fiber positioning and fixing groove; a clampmember which presses said cover member toward said base member; and awedge insertion portion into which a wedge for pressingly separatingsaid cover member and said base member from each other can be inserted,said method comprising the steps of:inserting said wedge into said wedgeinsertion portion to form a space into which the optical fiber can beinserted, between said base member and said cover member; inserting theoptical fiber from a rear side of said optical connector until theoptical fiber abuts against said short optical fiber; and detaching saidwedge to attach said optical connector to a terminal of the opticalfiber.